Increasing awareness of the effects of vehicle exhaust emissions and the like has resulted in regulations to control these emissions. In particular, various federal and state on-board diagnostic regulations (e.g., OBDII) require that certain emission related systems on the vehicle be monitored, and that a vehicle operator be notified if the system is not functioning in a predetermined manner. Automotive vehicle electronics therefore include a programmed diagnostic data manager or the like service configured to receive reports from diagnostic algorithms/circuits concerning the operational status of various components or systems and to set/reset various standardized diagnostic trouble codes (DTC) and/or otherwise generate an alert (e.g., MIL). The intent of such diagnostics is to inform the operator when performance of a component and/or system has degraded to a level where emissions performance may be affected and to provide information (e.g., via the DTC) to facilitate remediation.
In this regard, the California Air Resources Board (CARB) requires monitoring for “irrational” sensor values. A sensor value may be considered irrational when it is outside of a range of allowed normal performance. Rationality diagnostics rely on other system performance signals to evaluate the accuracy of the sensor signal undergoing the rationality test.
Two examples of rationality tests include an intake air temperature (IAT) skewed low test and an engine coolant temperature (ECT) range low-limited test. As to the IAT test, one characteristic evaluated is whether the measured IAT is skewed relative to what it should or is expected to be (i.e., skewed high or skewed low), for example, as seen by reference to U.S. Pat. No. 7,120,535 entitled “METHOD AND APPARATUS TO EVALUATE AN INTAKE AIR TEMPERATURE MONITORING CIRCUIT” issued to Rahman et al, owned by the common assignee of the invention and hereby incorporated by reference in its entirety.
Rahman et al. disclose a method for performing an IAT (skew low) rationality test that involves comparing the IAT measurement with an engine coolant temperature (ECT) measurement under circumstances where they are expected to be about the same. For example, start-up IAT and ECT measurements should generally be the same after a long (e.g., greater than 6 hours) “soak” in cold environments (i.e., when a vehicle is exposed to ambient air temperatures, with its ignition turned off and thus has been allowed to cool off). If there is a large temperature offset (e.g., >20° C.) between the start-up IAT and ECT after adequate soak time, the IAT rationality test assumes that the IAT sensor output signal is skewed, and then conducts a secondary drift check. The purpose of the secondary check is to determine if the large temperature offset is caused by a skewed sensor (which should fail the test) or rather by non-stabilized ambient conditions (which should not fail the test). Rahman et al. further disclose that the secondary check involves subsequent monitoring of the IAT sensor output for a predetermined amount of time, constantly comparing new IAT readings with the start-up IAT. If the subsequent IAT reading(s) do not show sufficient change within the predetermined time, the IAT rationality test will conclude that the IAT sensor/output is skewed and a failure will be reported. However, if there is sufficient change in the IAT, no report is made, on the belief that unstable ambient conditions caused the initial skew between the start-up IAT and start-up ECT. When certain conditions are met (e.g., a recurrence of the detected IAT skew), a failure code or other indication may be generated (i.e., a DTC “P0111-IAT Circuit Range/Performance Problem” flag may be set).
A problem, however, exists in the art. As background, it is known to provide an engine block heater on certain vehicles, which is a desirable feature especially in colder climates. In cold operating temperatures, the engine can suffer slow engine cranking speed and unstable combustion. The slow cranking speed is caused primarily by the inherent higher viscosity of the engine lubricating oil, reduced frictional bearing clearances as well as reduced battery performance. The engine block heater is typically deployed as a heating element or the like located in the engine block. The engine block heater is operated, typically from an external alternating current (AC) power source, for heating the engine block and thus also heating up the engine coolant contained in the block. Increasing the engine coolant temperature reduces the impact of viscosity and bearing clearances (although battery performance is not directly affected). Accordingly, the use of the block heater facilitates cold starting, among other benefits.
Operation of the engine block heater, however, can confuse the IAT and ECT rationality diagnostics. Testing has shown that the engine block heater can (1) raise the engine coolant temperature (ECT) as much as 50° C. above ambient and (2) raise the intake air temperature (IAT) as much as 20° C. above ambient. This results in a temperature offset at start-up between IAT and ECT by as much as 35° C. after an ample soak time. Thus, a conventional IAT rationality test, in view of this temperature difference, would conclude that there is a rationality problem with the IAT sensor output, since it is skewed to the low side of the ECT. This conclusion, however, is erroneous. Moreover, since the engine block heater is operated from externally-provided AC power, it is not possible for an engine control unit (ECU) or the like to directly detect if an engine block heater was operated during soak. It is important for the reliability of certain rationality tests (including the IAT and ECT tests mentioned) to be able to determine if an engine block heater has been used during soak.
There is therefore a need for a system and method for detecting the presence (operation) of an engine block heater that minimizes or eliminates one or more of the problems set forth above.